95 The first of these circuits can be conceptualized as an excitatory triangular circuit, whereby the basolateral nucleus of the amygdala and the orbital and medial prefrontal regions are interconnected by excitatory (especially glutamatergic) projections with each other and with the mediodorsal nucleus.96-100

This means that increased metabolic activity in these structures would presumably reflect increased synaptic transmission through the limbic-thalamo-cortical circuit. The limbic-striatal-pallidal-thalamic circuit constitutes a disinhibitory Inhibitors,research,lifescience,medical side loop between the amygdala or PFC and the mediodorsal nucleus. The amygdala and the PFC send excitatory projections to overlapping Inhibitors,research,lifescience,medical parts of the ventromedial striatum.101 This part of the striatum sends an inhibitory projection to the ventral pallidum,102 which in turn sends GABAergic (GABA, γ-aminobutyric acid), inhibitory Apoptosis inhibitor fibers to the mediodorsal Inhibitors,research,lifescience,medical nucleus.99 Figure 2 Altered metabolism in the prefrontal cortex (PFC) ventral to the genu of the corpus callosum (c.c.) (ie, subgenual PFC) in mood disorders. A.

Negative voxel t values where glucose metabolism is decreased in dépressives relative to controls in … Implications for the pathogenesis of emotion dysregulation The circuits described above have also been implicated in the depressive syndromes arising secondary to lesions or degenerative Inhibitors,research,lifescience,medical illnesses. Lesions involving the PFC (eg, tumors or infarctions) and the diseases of the basal ganglia, (eg, Parkinson’s disease or Huntington’s disease) are associated with higher rates of depression than other similarly debilitating conditions and result in dysfunction at distinct points within these circuits and affect synaptic transmission in diverse ways.103 Consistent with this Inhibitors,research,lifescience,medical hypothesis, imaging studies of depressive syndromes

arising secondary to neurological disorders have generally shown results that differ from those reported for primary mood disorders. For example, in contrast to the findings of increased CBF or metabolism in parts of the orbital see more cortex in primary depressives, orbital cortex flow is reportedly decreased or not significantly different in subjects with depressive syndromes arising secondary to Parkinson’s disease, Huntington’s disease, or basal ganglia infarction relative to nondepressed subjects with the same illnesses.104-107 Primary and secondary depressive syndromes may thus involve the same neural network, although the direction of the physiological abnormalities within individual structures may differ across conditions.